Japan's government has denounced as "absolutely unacceptable" a radiation-level reading error by the operator of the earthquake- and tsunami-hit Fukushima atomic plant.

Top government spokesman Yukio Edano put forward the criticism today -- one day after the plant's operator, the Tokyo Electric Power Company, said water at the site had reached 10 million times the normal level.

Officials later said the calculation was erroneous -- although radiation levels in the area remain dangerous.

Work to stabilize the damaged reactors at Fukushima has been disrupted as radiation from the plant has leaked into the air and Pacific Ocean and contaminated local farm produce and drinking water. Officials, however, say the levels are not high enough to pose an imminent threat to people in the region.

In another development, a 6.5-magnitude earthquake struck today off the coast of northeastern Japan -- the same area that was devastated by the earthquake and tsunami.

The quake prompted authorities to issue a tsunami alert for Miyagi Prefecture -- but no wave emerged and there were no reports of serious damage or injuries.

The official death toll from the March 11 magnitude-9.0 quake and tsunami is now more than 10,600, with some 16,500 people still listed as missing.